1. Field of the Invention
This invention relates to a method of providing an earth covering useful for water harvesting. The method provides a cloth reinforced elastomeric silicone membrane, impervious to water, that lines a depression suitable to direct, transport, or hold water and prevents the loss of water into the earth.
2. Description of the Prior Art
Water harvesting is a technique for developing local water supplies for such things as livestock, wildlife, runoff farming, and domestic use. Ancient desert farmers cleared hillsides and smoothed the soil to increase the amount of rain water that flowed down the hill. Contour ditches carried the runoff to lower lying fields where the water was used to irrigate crops.
In more recent history, the collection of rainwater from the roofs of homes and its storage in a cistern was common practice until the widespread development of central water systems in cities.
Systems have been evaluated for collecting water supplies for livestock in semiarid rangeland. Mikelson has reported on the use of metal sheeting, butyl rubber sheeting, asphalt roofing, and soil-bentonite mixtures as methods of collecting water for transportation to storage areas. Mikelson's report in "Proceedings of the Water Harvesting Symposium, Phoenix, Arizona, Mar. 26-28, 1974," published by the Agricultural Research Service, U.S. Department of Agriculture, indexed as GPO791-043, pages 93 to 102, concludes that water harvesting catchments tested can be useful, but the costs are high. The effects of weathering reduces the useful life of all methods. High winds and sunlight tend to destroy the covering materials. McBride and Shiflet report in the same reference, pages 115 to 121, on water harvesting catchments of various types, including glass fiber-asphalt constructions. Those glass fiber-asphalt constructions coated the soil, after sterilization, with glass fiber mat which was then coated with cationic liquid asphalt emulsion and overcoated with roofing type clay asphalt emulsion. The emulsion requires replacement at 3 to 5 year intervals. The surface was often broken by plants, burrowing rodents and ants. Dedrick reports in the same reference on storage systems at pages 175 to 191. In addition to methods mentioned above, he discusses the use of plastic film, ethylene-propylene rubber and chlorosulfonated polyethylene sheeting, and hard surface linings such as portland cement concrete. The rubber coatings must be protected from mechanical damage and weathering. The hard surface linings are expensive to install and subject to damage from alternating freezing and thawing.
In the same reference, at pages 76 to 83, Plueddemann reports on testing under laboratory conditions a variety of latex polymers and water repellants for suitability for treatment of soil to improve water harvesting. His recommendation is a mixture of an SBR latex mixed with an emulsion of silicone fluid. Experiments are given to show usefulness, but all work was in a laboratory as experiments. In his conclusion he states that the silicone emulsion alone is completely ineffective, but is a very effective water repellent when mixed with a suitable polymer latex.
A companion technique for the development of local water supplies is the use of canals or ducts to transport water from an available source to the desired predetermined location. The source, of course, must be located high enough above the predetermined location so that the water will flow with sufficient velocity to deliver the required amounts. Canals, aquaducts, and irrigation ditches have varied in construction from earthen ditches to concrete lined ditches and masonry aquaducts. Lining ditches with concrete is difficult and expensive, so it has been primarily confined to large canals. In small ditches or ducts as used in irrigation systems, the cost of concrete linings is prohibitive.
An earthen ditch such as used in irrigation systems can waste a majority of the water that enters the system. Water soaks into the walls and bottom of the ditch all along its length. Wet soil along the ditch readily grows vegetation which further uses additional water through transpiration. Vegetation growing under the water surface further retards the flow of water through the ditch, exposing the water to further losses through evaporation. Water lost during transporting from source to the use location is wasted. In arid locations such waste may be of great importance due to the lack of sufficient water at the source to make up for the loss in transporting.